Development and Evaluation of Bituminous Mixes Containing Reclaimed Asphalt Pavement and Recycled Concrete Aggregate

Abstract

Due to increased maintenance and rehabilitation activities related to bituminous pavements, huge quantity of aged bituminous mix is generated as waste, needing huge space for disposal/dumping. This waste is commonly referred to as reclaimed asphalt pavement (RAP). The RAP material normally contains substantial amounts of aggregates and bitumen. The latter is found to have lost most of its desirable properties in course of its service. It is also of great concern that, due to unabated construction activities, aggregates used in bulk in road paving layers become scarce and costlier because of the fast depleting natural stone resources. Keeping these two issues in mind, a good number of attempts have been made to re-use these pavement wastes, thus reducing the cost of construction as well as preserving the available natural stone resources. Concrete is a commonly used material for buildings and also for different types of structures. The demolition of such concrete structures because of end of their service life or any other reason, results in huge amount of construction and demolition waste. The disposal of such concrete demolition wastes requires huge space for dumping. When these concrete wastes are recycled and turned into aggregates for new construction works, these are known as recycled concrete aggregate (RCA). Similarly, plastics which are used in day-to-day activities remain as wastes once they are used. These plastic wastes being non-biodegradable adversely affect the environment.
It is reported that, both RAP and RCA have been separately used in bituminous pavements with promising results. But a study on the combined effect of RAP and RCA in bituminous paving applications has not been done systematically. The scholar has therefore been motivated to use RAP and RCA each collected and processed locally for development of new bituminous paving mix through a simple and innovative approach. The approach involves recovering bitumen from the RAP and addition of fresh bitumen suitably to the extracted bitumen (from RAP) in order to achieve the desired conventional and rheological properties of the target bitumen conventionally used in India, so that RAP may be reused as new bituminous paving mix. Though many researchers have used different rejuvenators to modify the aged binder characteristics, the present study involves the use of low viscosity VG10 and VG30 bitumens each in appropriate proportion for achieving the normal binder consistency as that of target VG40 bitumen. Further, it was felt necessary to develop and evaluate the resulting dense bituminous macadam (DBM) mixes containing mainly RAP and additional ingredients such as aggregate and virgin bitumen of low viscosity, with all ingredients in selected proportions. A new general approach was developed to determine the quantity of fresh aggregates and virgin low viscosity bitumen to be added to RAP to suit the existing aggregate grading of RAP, RAP bitumen content and the selected proportion in modified bitumen blend. The tests used for evaluation included Marshall characteristics, indirect tensile strength, moisture susceptibility, fatigue life and rutting resistance. For the purpose of comparison a control mix having same aggregate grading, made of conventional stone aggregate (CSA) and VG40 bitumen was also considered. Further, attempts have been made to replace the conventional coarse aggregate fractions in modified RAP mixes by RCA and pretreated recycled concrete aggregate (PRCA). As a part of further development, waste plastic in the form of low density polyethylene packaging for milk (500 ml pouches) available locally and abundantly, were utilised to further modify the resulting paving mixes.
Based on penetration tests initially corroborated by other conventional and rheological tests, the optimum proportions of the modified blend comprising VG10 or VG30 bitumen and RAP bitumen were found to be 60:40 and 70:30 respectively. As compared with virgin bitumen, the modified bitumen binder also resulted in improved resistance to rutting at high service temperatures, and better resistance to fatigue against the RAP bitumen at intermediate performance temperatures. Marshall characteristics and moisture susceptibility parameters indicated that 30% RAP for VG30 and 40% RAP for VG10 can be considered as optimum dosages for the modified RAP mixes (containing additional CSA, RCA or PRCA), which can perform either similar or better than the control mix (CSA-VG40). Modified RAP mixes prepared with RCA/PRCA and waste plastic (designated respectively as RAP-RCAP/ RAP-PRCAP) were observed to have better Marshall characteristics than the control mix, especially in terms of Marshall stability and flow value. Utilisation of waste plastic in modified RAP mixes can be less susceptible to moisture induced damage. Use of pre-treated RCA and RAP in the bituminous mix was found to be effective with decreased rut depth and higher flow number in contrast with the control mix. Utilisation of waste plastic in all categories of modified RAP mixes considered in the study further enhances the rutting resistance as determined in terms of flow number and rut depth. The modified RAP mixes with pretreated RCA and waste plastic (RAP-PRCAP) were also observed to have significant improvement in terms of resilient modulus as well as fatigue life than the control mix at all test temperatures. This indicates a major benefit of using RAP, pre-treated RCA and waste plastic in the resulting bituminous paving mixes. Besides, the modified RAP mixes prepared with pre-treated RCA and waste plastic in dense bituminous macadam (DBM) layer of flexible pavement can reduce the total cost of the pavement (up to 15%, for a service period of 30 years) as compared with conventional bituminous mix (control mix).
On the whole, this study recommends 30%RAP-PRCAP-VG30 and 40%RAP-PRCAP-VG10 mixes (each with 8% plastic by weight of respective optimum bitumen content) have much superior performance characteristics than the control DBM mix with conventional stone aggregate and VG40 bitumen. It is concluded that, this combination of waste materials such as RAP, RCA and waste plastic can be reutilised in place of control bituminous paving mixes with improved performance characteristics, which can lead to sustainable bituminous paving ensuring economy, conservation of natural resources and reduction of environmental concerns. The utilisation of RAP and RCA modified with waste plastic in a fresh bituminous paving mix, is a new and original contribution of the present study.